Embryology

Question 1

What are the 3 stages of life before birth and their timings?

Answer 1

1) Preimplantation stage-week 1.
2) Embryonic stage (organogenesis) Weeks 2-8.
3) Foetal stage (growth and development). Weeks 9-38.

Question 2

What is cleavage?

Answer 2

Occurs during week 1. It is mitotic divisions of the fertilised oocyte. However, the overall size remains the same, this allows its passage down the narrowest bit of the fallopian tube, the isthmus.

Question 3

What is a morula?

Answer 3

Occurs around day 4 after fertilisation, cells maximise their contact with each other, forming a cluster of cells held together by tight junctions- compactation.

Question 4

What are the 3 extra- embryonic membranes?

Answer 4

Amnion, Yolk sac and chorion. In the early embryonic period they are associated with “feeding” the embryo by diffusion.

Question 5

Give details about the amnion.

Answer 5

Continuous with the epiblast. Persists right until birth and is the cavity fills with amniotic fluid which is protection for the developing embryo.

Question 6

Give details about the yolk sac.

Answer 6

Continuous with the hypoblast. Important in nutrient transfer in weeks 2-3 and disappears around week 20.

Question 7

Give details about the chorion.

Answer 7

The trophoblast and the extraembryonic mesoderm. Forms the foetal component of the placenta. Chorionic cavity is seen in early pregnancy by disappears when the amnion expands.

Question 8

Define ‘gastrulation’

Answer 8

A process of cell division and migration resulting in the formation of the three germ layers.

Question 9

What is a teratoma?

Answer 9

A tumour with tissue or organ components resembling derivatives of the 3 germ layers. Can be malignant or benign.

Question 10

What does neurotrophin-3 do?

Answer 10

Directs the dermatome to become dermis from dorsal neural tube.

Question 11

What is the lateral somitic frontier?

Answer 11

Well defined border between each somite and the lateral plate mesoderm.

Question 12

What innervates Epaxial muscle?

Answer 12

Epaxial (true back muscles) are innervated by the dorsal primary rami.

Question 13

What innervates Hypaxial muscle?

Answer 13

Hypaxial (limb and body wall) are innervated by ventral primary rami.

Question 14

When does limb rotation occur and what happens?

Answer 14

It occurs during week 7. The upper limb rotates 90 degrees laterally. The lower limb rotates 90 degrees medially.

Question 15

What is an anomaly?

Answer 15

Something that deviates from the normal or expected.

Question 16

What does congenital mean?

Answer 16

A disease or physical anomaly present from birth.

Question 17

What is a teratogen?

Answer 17

An agent or factor which causes malformation of an embryo.

Question 18

What causes Rickets?

Answer 18

Defective mineralisation or calcification of bones due to impaired vitamin D metabolism.

Question 19

What is developmental dysplasia of the hip?

Answer 19

Poorly developed acetabulum and head of femur in utero. Dislocation common occurs after birth-avascular necrosis of the femoral head may be a complication. Treated with a Pavlik harness.